Sailboard with slotted winglets

ABSTRACT

A sailboard hull has at least one pair of winglets or foils beneath the top of the board. Each winglet or foil has above it a slot and allows dynamic lift from both the top and bottom surface of the winglet and reduction of drag when the board is traveling at a transition speed between displacement mode and planing mode. At high planing speed it does not normally have lift from the top surface of the winglet. There may be multiple pairs of winglets or foils. Back slots may be provided at the rear of the sailboard hull providing a higher ratio of winglet width to maximum hull width. A top slot may cover at least half the winglet area, and a winglet may have a camber/slope step on the planing surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/880,360, filed Sep. 13, 2010, which is acontinuation-in-part of International Patent ApplicationPCT/US2009/057138, which claims priority of U.S. Provisional PatentApplications 61/097,836, filed Sep. 17, 2008, and 61/165,472, filed Mar.31, 2009, the priority of the filing date of which applications ishereby claimed. U.S. patent application Ser. No. 12/880,360 also claimspriority to International Patent Application PCT/US10/29785, filed Apr.2, 2010, which claims priority to U.S. Provisional Patent Application61/166,569, filed Apr. 3, 2009. All of these references are hereinincorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to a sailboard/windsurfer hullor other small watercraft hull having winglet(s) with a slot forimproving the transition from displacement operation to planingoperation and the transition to higher planing speeds.

BACKGROUND

U.S. patent application Ser. No. 10/157,875 teaches the use of wingletson the outer surfaces of a sailboard for increasing the lift to drag ofthe sailboard when transitioning from a displacement mode to a planingmode. These winglets have been found to be quite effective in reducingthe amount of wind needed to cause the sailboard to plane. However, thefront nose of these winglets can be above the flat undisturbed watersurface thus preventing or reducing the water flow and lift from the topsurface of the winglet.

When the sailboard is designed so that the water will easily pass abovethe front of the winglet, the board needs to be slightly concave downand slightly longer in the nose. One would also like the lift from thewinglet to be nearer the back of the board. Also, the flow over the topof the front of the winglet may stop at a slower board speed thandesired, while the camber of the winglet is limited by the thickness tolength ratio. In addition, one would like the winglet to be a largerpercentage of the back of the board to further reduce the wave andturbulent drag at transition speeds.

U.S. patent application Ser. No. 10/157,875 also teaches the use of awing grid which is a plurality of winglets with slots between thewinglets. However, each winglet has drag from the separation of thewater at its nose to pass over and under the winglet, thus if the numberof winglets is too large there will be increased drag from this winggrid.

On wings of many airplanes there are “Fowler-type flaps” which, whenthey are moved down and back from the wing, form slots in front of theflap or winglet with a surface of the main wing. At some positions ofthese flaps, the top part of the wing in front of the slot partiallycovers the nose or beginning of the flap. In this position there is aCoanda flow of energized fluid that flows through the slot and over theflap thus creating a vacuum lift on top of the flap.

PCT/US2009/057138 teaches a step design whereby at slower planing speedsthe water contacts the surface close to and behind the step, producinglift. At faster planing speed it does not contact this surface, thusreducing drag.

U.S. Pat. No. 3,495,563 to E. Reischmann shows in FIGS. 2 b and 2 d awinglet or part of a planing surface (31) on a planing watercraft. Abovethis winglet/planing surface (31) there is not a slot but rather onlythe side of the remaining part of the hull with a dead rise of about 45degrees. The stated purpose is to reduce the drag.

SUMMARY

It is therefore an object of the present invention to provide asailboard hull to increase the dynamic lift of a winglet beneath a slotin the side of the sailboard hull.

It is another object to have an efficient winglet on a shorter orsmaller sailboard.

It is a further object to move the lift further back closer to, orbehind, the center of gravity of the board and sailboarder.

It is yet another object of the present invention to have the nose of awinglet covered such that water from the front of the winglet does notspray up onto the sailboarder.

Another further object of the invention is to have the top of a wingletclear of water above about 15 mph.

It is still another object of this invention to reduce the variation ofthe optimum position of the center of gravity of the sailboard andsailboarder.

Another further object of the invention is to prevent weeds fromcatching in the slot.

To achieve the foregoing and other objects and advantages of theinvention, winglets with a forward slot, including a slot opening, inaccordance with the invention, start at a location on the order of 130cm, generally in the range of 110 to 210 cm, from the back of asailboard or less. That is where, when the sailboard is transitioningfrom displacement mode to a planing mode, the pressure under the boardis near the maximum where the slot opens in front of the winglet. Thisopening of the slot in front of the winglet may be on the order of 50 cmlong (range of 20 to 120 cm) as measured parallel to a longitudinal axisof the board. In an exemplary embodiment, the vertical distance (height)of the slot between a top surface of the winglet and a bottom of thesurface above the winglet is roughly one-half the thickness of thewinglet, especially at a front opening to the slot. A surface startingbefore the nose of the winglet (i.e. the front/leading edge of thewinglet) can extend and be integral with at least a portion of a surfaceabove the winglet. The surface starting before the nose of the wingletmay extend over the winglet from the nose of the winglet back to a pointwhere the winglet has a thickness of about 50% the maximum thickness ofthe winglet.

The thickness of the winglet may vary, either or both in a transversedirection and a longitudinal direction. This can result, for example, inthe nose and/or outside edge of the winglet having thicknesses which arethinner than at other points of the winglet. The nose of the wingletmay, for example, have a thickness of about 50% (half) the maximumthickness of the winglet. This reduces spray off of the nose of thewinglet. Meanwhile, the slot allows energized water from under the frontof the board to produce a Coanda effect (lift) over the top surface ofthe winglet.

The winglets according to this invention may have a slot formed on thetop of (that is to say, above) a portion or the entirety of the winglet,particularly near the end of the winglet such that the turbulence andwave drag at the back of the board is decreased. That is, a top slotallows the winglet to be extended under a top portion of the board(under a hull part having a top surface on which a user stands or issituated when using the sailboard and a bottom surface forming a slotwith the winglet.) This also allows the top surface of the sailboard,which is above the top slot, to have a foot strap and a larger topsurface area for sailing and jibing the sailboard.

The transverse end of a forward slot, i.e. the outside, can be coveredor partially covered so that water and waves, particularly on thewindward side do not enter the slot or strike the nose of the wingletwhen sailing at high planing speeds, such as over 15 mph. When partiallycovered by a cover or partial cover (which can be part of the hull), anopening/gap between the cover or partial cover and the winglet can beprovided to allow any weeds or grass which enter the slot to escape.

While the nose of the winglet can be perpendicular, angled back, angledforward, or curved, it is preferred that it be angled or swept back.This will both allow it to shed weeds and direct the water passing ontop of the winglets away from the front foot straps.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, and advantages will be betterunderstood from the following detailed description of a preferredembodiment of the invention with reference to the drawings, in which:

FIGS. 1A-1E show, respectively, a curved and angled cross-sectionalview, top plan view, side view, bottom plan view, and a transversecross-sectional view of a sailboard hull with slotted winglets,

FIG. 2 shows a side view of a sailboard hull with multiple slottedwinglets with a camber/slope step,

FIG. 3 shows a sailboard with a cover over a front slot opening whichextends over the top of the winglet,

FIG. 4 shows a detail of the camber/slope step in FIG. 2, and

FIGS. 5A-5E show, respectively, a top plan view, a side view, and threetransverse cross-sectional views of a sailboard hull with a winglet witha top slot or channel.

DETAILED DESCRIPTION

Referring now to the drawings, and more particularly to FIGS. 1A-1E, across section of a side part of a sailboard hull 1 is shown with apreferred embodiment of a winglet 2 with a front slot 3 and a top backslot 6. ‘Front slot’ and ‘forward slot’ are treated as substantiallysynonymous terms and may be used interchangeably herein. A ‘front slot’or ‘forward slot’ may include an ‘opening’ or ‘forward opening’ whichshould also be understood as substantially synonymous. The term ‘topslot’ includes ‘back slot’ and ‘top black slot’. Hereafter a ‘winglet’ 2may also be called a ‘slotted winglet’ 2 to emphasize the presence of aslot above the winglet. Winglet 2 has a length, in a longitudinaldirection of the sailboard hull, at least 2 or 3 times its transversewidth on each side of attachment to the main body. Thus it isdistinguished from a fin or skeg at the side of the hull as in someracing catamaran sailboats. Winglet 2 may be integral with the sailboardhull such that the hull of the sailboard includes the winglet. Theportion of the sailboard hull excluding the winglet will be referred toas the main board (or hull) body.

A slot as used herein is a narrow opening, groove, passage, or channelformed between a winglet or foil and a surface of the hull such that theheight to width ratio of the slot is less than one, and the height towinglet chord ratio is much less than one (and thus less than the heightto width ratio). Furthermore, a surface which forms a top or roof of theslot is substantially flat in the transverse direction. Substantiallyflat is defined as having a slope equal to or less than ±15° andpreferably equal to or less than ±10° with respect to a horizontal. Asused, the symbol “+” indicates that the top/roof of a slot slopes up andout (that is, angling up with respect to a horizontal in a transverseplane and away from a longitudinal center line of the hull). This issimilar to the dead rise convention of a hull, except that the angle ofa dead rise is usually larger than applicable to form a slot. The symbol“−” indicates the top/roof of a slot slopes down and out (that is,angling down with respect to a horizontal in a transverse plane and awayfrom a longitudinal center line of the hull).

A front slot 3 starts behind a front planing or displacement section 4,which may be part of the nose or front of a sailboard. The opening/startto a front slot 3 is located in a region of an underside of thesailboard hull where water pressure is highest when the sailboard startsto plane. For a nearly flat planing surface, this maximum pressureoccurs at about 1/10th the wetted surface length back from the start ofthe wetted surface length. Winglets with a forward slot may start at alocation on the order of 130 cm, generally in the range of 90 to 160 cm,from the back of a sailboard or less. When the sailboard istransitioning from displacement mode to a planing mode, the pressureunder the board is near the maximum in the slot at its opening in frontof the winglet. The slot opening in front of the winglet 2 is 20 to 120cm, or on the order of 50 cm, in a longitudinal direction of the board.

“Planing mode” is defined as the lift being mainly hydrodynamic lift(≧90%) and when the hydrostatic lift is ≦10% of the total lift.“Displacement mode” is where the lift is mainly hydrostatic and the dragvs. speed is increasing nonlinearly with increasing speed. As usedherein, “displacement mode” is used to indicate that ≧70% of the lift ishydrostatic lift and the remaining lift (≈30% or less) is hydrodynamiclift. Thus the board is in “transition mode” when the hydrostatic liftis between 70% and 10% of the total lift and the hydrodynamic lift ismost of the remaining lift, that is 30% to 90%. In “transition mode”,the drag vs. speed normally goes through a hump or peak, but this is notalways the case if the weight is small or the wave drag is sufficientlyreduced.

In transition mode, the high water pressure forces water through a frontslot 3 and over the top surface of a winglet 2. This causes a Coandaeffect/vacuum lift on the winglet.

The main drag forces acting on a hull in planing mode are dynamic drag,which is the dynamic force in the backward direction, and skin friction.The main drag force acting on a hull in displacement mode is wave drag,which is the difference of pressure on forward facing surfaces andbackward facing surfaces. In transition mode, all three—that is to saywave drag, dynamic drag, and skin friction—are significant, with wavedrag and dynamic drag being the most significant.

The lift of the water going through front slot 3 and top slot 6 (or slot10 of FIGS. 3 and 5A-5E) is not large and is less than the planing lifton the winglet. This is due to the fact that the depth and mass of thiswater is small and not like the depth and mass of the fluid over anormal wing on an airplane or a deep hydrofoil on a watercraft.

It should be noted that the cross section of the board shown in FIG. 1Ais angled/curved, as shown by section A-A in FIG. 1B. The cross sectionis slightly angled/curved to approximate more closely the path of thewater at a transition speed. Dynamic lift can be provided from both thetop and bottom surface of the winglet when the board is traveling at atransition speed between displacement mode and planing mode.

At high planing speed the board does not normally experience lift fromthe top surface of the winglet, as water may not enter the slot at highangles of attack. When the board is planing at a high speed, waterleaving the front planing or displacement section 4 may go below thenose of the winglet. At high speeds, the front slot 3 and the nose ofthe winglet 2 may be above the water and thus only the bottom surface ofthe winglet is in or makes contact with the water. Front slot 3,provided with an opening in front of the winglet, allows for the wingletto start further back on the sailboard where the lift will be closer tothe center of gravity. Furthermore, the sailboard can be shorter ifdesired. This in turn makes the front of the sailboard lighter andimproves the ease by which a sailboarder or sailor can sail at anoptimum planing attack angle of about 3 to 5 degrees.

In an exemplary embodiment, the bottom edge or bottom 4′ of planing ordisplacement section 4, which is the start of the roof of the opening toslot 3, is approximately tangent (that is, less than or equal to) 10° toa tangent line to the front planing or displacement section 4, as shownin FIG. 3. Alternatively, the bottom edge or bottom 4′ of section 4 canhave a smooth upward curvature (rocker) such that the water will remainin contact with both the top and bottom surfaces of the winglet 2 at atransition speed, but the water flow from waves will separate from thecurvature and go below the nose of the winglet 2 at faster planingspeeds.

The surface behind the upward curve of bottom 4′ on section 4 whichprovides the roof of the opening to slot 3 is preferably cambered with anegative second derivative (height with respect to longitudinaldistance) curvature as shown in FIG. 3. This roof surface can end at orjust after covering the nose of winglet 2 as shown in FIG. 1A. In someembodiments this roof may instead be straight.

Winglets 2 with a forward slot 3 in accordance with the invention startat a location on the order of 130 cm, generally in the range of 90 to160 cm, from the back of the sailboard. That is where the pressure underthe board is the greatest when the sailboard is transitioning fromdisplacement mode to a planing mode. The forward slot 3 opening in frontof a winglet 2 may be roughly 50 cm long (range of 20 to 120 cm) asmeasured along the bottom of the winglet in the longitudinal directionof the board. The vertical distance (i.e. height) at the opening of aforward slot 3 between a winglet 2 and a surface which provides the topof forward slot 3 may be roughly one half the maximum thickness of thewinglet or greater.

As shown in FIG. 1A, at the opening of forward slot 3, the surface thatmakes the top of forward slot 3 is the lower surface of section 4. Thissurface extends over the nose of the winglet to a point where thewinglet thickness has increased to a thickness of about 50% of themaximum thickness of the winglet (prior to reaching the point of maximumthickness of the winglet). Thus any water spray from the nose of thewinglet is reduced. That is to say, a portion of front planing ordisplacement section 4 extends over a nose or leading edge of eachwinglet or foil such that spray off from the nose or leading edge of thewinglet or foil is reduced as compared to spray off of a nose or leadingedge of a winglet or foil which does not have a portion of a frontplaning or displacement section extending over it. The forward slot 3allows energized water from under the front of the board (leavingsection 4) to produce a Coanda effect over the top surface of thewinglet.

Referring now to FIGS. 1B to 1D, FIG. 1B shows a top view, and FIG. 1C aside view, of a sailboard and the location of the cross section shown inFIG. 1E. The transverse end of a forward slot 3 can be fully orpartially covered, such as at the opening of the forward slot 3, by acover 12 so that water and waves, particularly on the windward side ofthe sailboard, do not enter the forward slot and strike the nose of thewinglet when sailing at high planing speeds, such as over 15 mph. Whenpartially covered by cover 12, an opening between partial cover 12 andthe winglet can allow weeds going into the forward slot to escape. FIG.1D shows a bottom view of the sailboard shown in FIGS. 1B to 10.

While a slot and winglet can be perpendicular, angled back, angledforward, or curved, it is preferred that they be swept back, preferablyat angles of 20° to 80°. This amount of sweep-back can allow theshedding of weeds or other solid debris which enter the slot, and aforward slot 3 which is swept back can direct the water passing over thewinglets away from the front foot straps and the board sailor.

A top slot 6 can be cut into the back of the hull of the sailboard. Thisallows the width of the back of the winglet to be a larger percentage ofthe back width of the board. This provides a higher ratio of wingletwidth to maximum hull width at the back of the winglet as compared witha front or middle of the winglet. Thus when the board is beginning toplane, a larger percentage of the water flowing under the top surface ofthe top portion 8 of the hull can flow smoothly off the back of thewinglet. The drag of the board at transition speeds is thereby reducedand the lift is increased. A top slot 6 also allows for a wider spacingof foot straps 26 and a wider top sailboard surface of the top portion 8of the hull, which can easily be used by the sailor for sailing andjibing the sailboard. The top slot 6 can have one or more support vanes6′ inside. These vanes are preferably curved to match the typical waterflow through a slot 6 at transition speed.

The board can have more than one set of slotted winglets, such as isshown in FIG. 2. FIG. 2 shows multiple slotted winglets. A main winglet2 is shown in the back. It may have a camber 16, step 21 and slope 18,i.e. a camber/slope step, on the planing surface. (Such features mayalso be employed on the winglet 2 of the embodiment discussed above inconnection with FIGS. 1A-1E as shown in FIG. 3.) In front of the mainwinglets 2 is a pair of auxiliary winglets 5. A main winglet 2 and anauxiliary winglet 5 are positioned so as to form a slot between them.The positioning can be a partial overlap of a tail/end of auxiliarywinglet 5 and a start/leading edge of main winglet 2, as shown in FIG.2. By the same token, section 4 extends over the auxiliary winglet 5 toform a further slot above auxiliary winglet 5. The slots thus formed arepreferably continuous and integral with the slot above main winglet 2.Tests of wings with auxiliary airfoils are given by Fred E. Weick andRobert Sanders NACA Report 472 pp 567-584. This arrangement of wingletsallows for a larger total slot height in front of the main winglet 2.Thus it allows more water to flow over the top of the winglet 2 attransition speed and a correspondingly larger lift coefficient. Both themain winglet 2 and particularly the auxiliary winglet 5 can start (i.e.have a leading edge) at a height above a center rocker line (i.e.centerline) 27 of the sailboard. This arrangement also allows the camber16 of the camber/slope step to be the whole length from near the start(i.e. leading edge) of the main winglet 2 to the step 21. The camber 16depth relative to the adjacent surface 24 can also be large, on theorder of 0.65 cm (range 0.02 to 2 cm), thus increasing the planing liftat high planing speed as well as total lift of the winglet 2 attransition speed. Part of the camber 16 can be above the hull depth atcenterline 27 of the hull and part can be below the hull depth atcenterline 27, near the step. The vertical dimension of the step 21 ispreferably about 2 to 3 mm (range of 1 to 9 mm), as shown at 7 in FIGS.2 and 3 and in the enlarged detail shown in FIG. 4.

The step 21 has a radius of curvature on the order of 1 cm. Behind thestep is a slope 18 which slopes upward. This allows smooth flow of waterover the step at transition speeds, and at roughly 15 mph or greater theflow of water behind the step dewets from slope 18. To insure thisventilation and de-wetting of slope 18 the outside edge of the wingletcan also be stepped with a horizontal displacement of about 1 cmrelative to the rail of the winglet 2 at the step 21. This is shown asedge step 41 in FIG. 1D, which for purposes of illustrating alternativeembodiments shows one side of the board with edge step 41 and one sidewithout. In practice, both sides of the board may have an edge step 41.

FIG. 2 shows the hull at a typical planing angle of attack of 3.5degrees (as measured with respect to a line tangent to the back 40% ofthe centerline 27 of the board body).

If desired, the auxiliary winglet 5 can be changed from a winglet andmade part of planing or displacement section 4. In such a case, a longslot/slot opening is produced. The resulting single slot isadvantageously stronger and easier to fabricate. This is what is shownin FIG. 3.

Referring now to FIG. 3, the length of a slot 10 over and on top of(i.e. above) a winglet 2 can be extended to the back of the board suchthat it would include slot 6 of FIGS. 1A-2. That is, a forward slot 3(of FIGS. 1A-2) can be integral and continuous with a back slot 6 so asto form a slot 10 extending to the back of the board. This configurationallows foot straps 26 on the top surface 8 of the sailboard to be placedfurther to the outside as in a Formula sailboard or other sailboards inwhich it is desired to use a longer fin.

As shown in FIGS. 1B-3, the back planing surface 23 of the winglet andsailboard bottom is outside of the planing region 24 near and in frontof a fin 9. The fin 9 is fixedly connected to the sailboard hull inplaning region 24. Back planing surface 23 includes slope 18. Slope 18can have a positive rocker on the order of a 30 meter (3000 cm) radiusor a positive second derivative of 3×10⁻⁴ cm⁻¹ (range of 0 to 8×10⁻⁴cm⁻¹). Alternatively, it can have a negative rocker. In addition, camber16 and planing surface 23 (which may further include a camber 25)produce lift at transition speed but dewet planing surface 23 behind thestep 21 at faster planing speeds. The bottom view of FIG. 1D shows twoplaning surfaces 23 and steps 21, each surface 23 being to either sideof back planing region 24.

The hull body may comprise planing regions 23 and 24. Alternatively,planing region 23 may be a planing region of a winglet, the wingletbeing integral with or fixedly attached to the hull body.

The depth of camber 16 can be small (about 2-6 mm) and consists of adownward curved section of about 10 cm length with a maximum angle onthe order of 7 degrees, as shown, for example, in FIG. 2 behind arrow28. This angle is formed between a first line tangent to camber 16 atthe end of camber 16 and centerline 27 at the same longitudinal positionof the board. The camber can also be larger, on the order of 0.65 cm(range 0.2-2 cm) as shown in FIG. 2. This camber is followed by a smoothupward curve with a radius on the order of 1 cm (range of 0.3 to 4 cm).These camber/slope steps allow the sailboard to be sailed at an optimumattack angle (3° to 5°) from transitional speeds to speeds greater than20 mph.

As disclosed in the above-incorporated PCT/US2009/057138 there should bean increased attack angle or cusp at least on the fin side of theintersection of the planing surface region 24 and the planing region 23.Planing surface region 24 is shown with dotted lines in the side view ofFIG. 1C to distinguish it from the rocker of surface region 23.

The bottom of the sailboard can be essentially flat near the fin, exceptfor a cusp 221 at the intersection between surface 23 and region 24.Since the purpose of cusp 221 is to keep the outflow of water fromplaning region 24 from wetting surface 23 in planing mode, its depthdepends on the transverse width of surface 23 and the verticaldisplacement of surface 23 above planing region 24. In some embodiments,the depth of step 21 relative to region 24 is small, and cusp 221protrudes down below both 23 and 24. This results in a downward cusp onboth surfaces 23 as well as region 24. The radius of curvature betweenthese two cusps can be on the order of 1 cm.

There can be multiple concave shapes or a slight “Vee” shape in region24 with variation of about 5 mm or less. Cusp 221 is also shown in theembodiment of FIG. 5E.

Since steps 21 are small, the region of the camber 16 and rocker/slope18 is shown in more detail in FIG. 4. The camber 16, step 21, slope 18and cusp are easy to fabricate into the bottom planing surface(s) of thesailboard. For example, they can be constructed from an additional pieceof Divinycell under the fiberglass or carbon skin of the sailboard.

If one wishes a particular sailboard to plane at lower speed, anothercamber 25 can be added at the end of the region 23 and slope 18. Camber25 preferably has a cup angle of 7 degrees or less, as shown in FIG. 4.In FIGS. 3 and 4, the hull is shown with a planing attack angle of zerodegrees.

Referring now to the front of the hull in FIGS. 1 a-3, the nose 30 ofthe hull of the sailboard is preferably shaped like an upside down orinverted wing, asymmetric from bottom to top with more transversecurvature on the bottom than on the top as shown in FIG. 1E. Thisinverted wing shape can be symmetric from the left side to the rightside (i.e. symmetric about a longitudinal section of the sailboard). Inthis way the top area shown as 31 can have less positive (e.g. convex)curvature or, preferably, a negative (e.g. concave) curvature as alsoshown in the exemplary cross-section of FIG. 1E, while the bottom area32 of the nose 30 will have greater curvature. A purpose of this noseshape is to reduce or counteract the lift of the true wind on the noseof the board, which can cause the sailboard to be unstable and the noseto fly up into the air. This effect is often referred to as board“tail-walking”. Thus, by employing an inverted wing nose shape, one canuse a larger sailboard and take advantage of the greater lift to drag ofthis invention.

FIGS. 5A-5E show an alternative winglet configuration 33. A winglet 33may have any desired aspect ratio of length to width and may be providedas a set of winglets. This set of winglets, a left winglet and a rightwinglet, have top slots 10 (channels 10) above winglets 33. Top slots 10cover at least half of the winglets 33. That is to say, a top/roof of aslot 10 covers at least half of the winglet surface which provides abottom/floor of the slot. FIG. 5A clearly shows a top portion 8 of thesailboard/hull, an underside of which provides the top/roof of slot 10,covering more than half of the top surface of winglet 33.

It is preferred that these winglets be swept back both to shed weeds andfor better directional stability. In FIG. 5A the front edge of eachwinglet 33 of the pair of winglets is swept back with respect to alongitudinal center line of the hull. The bottom of the end of winglet33 (i.e. the outside edge of the winglet; the part of the wingletfurthest from a longitudinal center of the hull), is below the bottomsurface of the rest of the hull, as shown in FIG. 5B. Winglet 33, morespecifically the bottom of the end of winglet 33, may be the lowest partor portion of the sailboard/sailboard hull, at that longitudinalposition.

With reference to FIGS. 5C and 5D, cross sections of two preferredembodiments of a sailboard hull with winglets 33 are shown. Thetop/upper surface of a top slot 10 preferably roughly follows the shapeof the top of the winglets so there is no pressure increase in thechannel due to a changing height in the slot/channel 10. At high planingspeed only winglet 33 and the back section of the sailboard, preferablywith camber/slope steps as discussed above, are in or in contact withthe water. Thus the winglets 33 with slots aid in the stability of thesailboard and maintaining the planing attack angle at high planingspeed. The cross sections in FIGS. 5C and 5D also show slot 10 coveringover half of a winglet 33. That is, the figures show the undersides ofthe top portion 8 of the sailboard covering over half of the topsurfaces of the winglet pair. In addition, the shape of a winglet 33 inthe transverse direction may be straight (such as in FIG. 5C) or bent orcurved (such as in FIG. 5D). In the latter case, the angle of thewinglet in the transverse direction may be greater where the wingletattaches to the remainder of the hull as compared to the end/tip of thewinglet. The end of the winglet may also slope up slightly. Note that inFIG. 5C, only the structural elements through which the cross-section istaken are shown for purposes of clarity. In FIG. 5D, however, someportions of the sailboard which are behind where the cross-section istaken are shown.

FIG. 5E shows a cross-sectional view taken near the rear of thesailboard. Rear slots 6 are present on either side of the sailboard.Support veins 6′, which appear behind the plane of the cross-section,are also shown. A small cusp 221 is present where each planing surface23 meets planing region 24.

Those skilled in the art will appreciate that two or more applicationsof winglets with a front slot or top slot can be used in a row inaccordance with the invention and that slotted winglets 2 can be usedwith known hydrofoils nearer the front or middle of a hull to bettermaintain an optimum planing angle at even faster planing speeds.

While the invention has been described in terms of a preferredembodiment and variations thereon, those skilled in the art willrecognize that the invention can be practiced with modification withinthe spirit and scope of the appended claims.

Furthermore, while the embodiments described herein are primarilydirected to sailboard hulls, those skilled in the art will recognizethat the invention pertains to other watercraft hulls, particularlysmall watercraft hulls, especially those with a length of 12 feet orless.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is as follows:
 1. A board hull of a sailboardor watercraft less than or equal to 12 feet long, comprising: a topportion which has a top surface and a bottom surface; at least one pairof winglets or foils at least a portion of which are beneath said bottomsurface of said top portion; and a slot above each winglet or foil ofsaid at least one pair of winglets or foils, wherein at least a portionof said bottom surface of said top portion is a roof of said slot and atleast a portion of an upper surface of said each winglet or foil is afloor of said slot, wherein said slot has an opening in front of orabove said each winglet or foil, and wherein water passing through saidslot reduces wave drag of said each winglet or foil.
 2. The board hullas recited in claim 1, wherein said slot has a height to width ratiowhich is less than one and a height to winglet chord ratio which is lessthan said height to width ratio.
 3. The board hull as recited in claim1, wherein said roof of said slot has a slope in a transverse directionequal to or less than ±15° with respect to a horizontal.
 4. The boardhull as recited in claim 1, further comprising: one or more front footstraps attached to said board top surface of said top portion, andwherein said slot and said each winglet or foil are swept back at anglesof 20° to 80° to allow shedding of weeds which enter said slot and/or todirect water passing over said each winglet or foil away from said oneor more front foot straps attached to said board top surface of said topportion.
 5. The board hull as recited in claim 1, wherein said at leastone pair of winglets or foils starts 90 to 160 cm from a back/rear ofsaid board hull.
 6. The board hull as recited in claim 1, furthercomprising: a pair of back slots cut into a back/rear of said board hullwhich are above at least a portion of said at least one pair of wingletsor foils, said pair of back slots being configured such that a ratio ofslot width to maximum hull width at a point at said back/rear of saidboard hull is equal to or greater than said ratio at a point furtherfrom said back/rear of said board hull.
 7. The board hull as recited inclaim 6, wherein each back slot of said pair of back slots has a supportvane positioned therein.
 8. The board hull as recited in claim 6,wherein said slot extends to said back/rear of said board hull such thatsaid back slots produce a streamline effect in displacement andtransition modes while said top portion forming a roof of said backslots allows the back foot straps to be spread wider apart and stillremain out of a water flow than without said back slots.
 9. The boardhull as recited in claim 6, further comprising at least two back footstraps, wherein said pair of back slots are configured to allow said atleast two back foot straps to be laterally spaced a distance equal to orless than a width of said board top surface of said top portion abovesaid back slots.
 10. The board hull as recited in claim 1, wherein abottom surface of said each winglet or foil has at least onecamber/slope step having a camber with a depth of 0.2 to 2 cm and a stepwith a height of 1 to 9 mm and a curvature of radius 0.3 to 4 cm. 11.The board hull as recited in claim 1, further comprising: a back planingregion near and in front of a fin at an underside of said board hull;and a back planing surface to either side of said back planing regionhaving a camber/slope step, an intersection of said back planing regionand said back planing surface, said intersection having a cusp, whereinsaid camber/slope step allows said board hull to maintain an attackangle of 3° to 5° for transitional speeds to speeds greater than 20 mph,and wherein said cusp keeps an outflow of water off said back planingregion from said back planing surface in planing mode.
 12. The boardhull as recited in claim 11, wherein said back planing surface has anadditional camber with a cup angle of 7 degrees or less.
 13. The boardhull as recited in claim 1, wherein said opening of said slot is 20 to120 cm long in a longitudinal direction of said top portion.
 14. Theboard hull as recited in claim 13, further comprising a front planing ordisplacement surface at a front bottom of said top portion, wherein aroof of said opening of said slot comprises i) a first part which isapproximately tangent said front planing or displacement surface, ii) asecond part having a rocker, and iii) a third part having a cambertoward and/or over a nose of said at least one pair of winglets orfoils.
 15. The board hull as recited in claim 1, wherein said roof ofsaid slot covers at least half of said upper surface of said eachwinglet or foil which is said floor of said slot.
 16. The board hull asrecited in claim 15, wherein said each winglet or foil is straight orbent/curved in a transverse direction.
 17. A watercraft hull,comprising: a top portion which has a top surface and a bottom surface;a winglet at least a portion of which is beneath said top portion; and aslot above said winglet formed by said bottom surface of said topportion and a top surface of said winglet, wherein said slot has aheight to width ratio which is less than one and a height to wingletchord ratio which is less than said height to width ratio.
 18. Thewatercraft hull as recited in claim 17, wherein said winglet isconfigured as a pair of winglets.